The present invention relates to disposable personal care products, such as diapers, feminine care products and adult incontinence products. More specifically, the invention relates to products having improved absorbent core integrity, and methods for producing such products through ultrasonic compressions.
Disposable care products are typically comprised of at least three general layers. These include an absorbent core placed between a liquid permeable inner liner and a liquid impermeable outer cover. The inner liner and outer cover can comprise one or more individual layers of materials, and additional layers can also be interposed between any of the general layers. For example, in the disposable diaper, the inner liner can comprise a surge layer consisting of thermoplastic fibers positioned beneath a thermoplastic mesh. Additionally, a tissue material, or wrap sheet, is often positioned between the outer cover and absorbent core, and between the surge layer and the absorbent core. At the diaper periphery, the material layers extending to the periphery are held together by conventional means, such as adhesives, crimping, fusing, or other methods known in the art.
The absorbent core receives and retains bodily fluids. It consists of a natural fiber batt that has a strong affinity for water and other hydrophilic components of bodily secretions. A dispersion of superabsorbent particles can also be incorporated into the fibrous core.
Maintaining a continuous, intact core, especially when these articles are used, is a recurring issue in the disposable garment industry. Breaks in the continuum of the core create open spaces that prevent the transport of fluid into the core, and the wicking of the fluid in the core. This breakdown of the core structure can cause fluids to leak out of the periphery of the diaper. The core breakdown also results in its sagging, which is visually unappealing to the consumer.
In the disposable diaper, adhesives used to bond various material interfaces within the diaper have not eliminated the breakdown of the absorbent core. The adhesive is conventionally applied in a swirl, spray or bead pattern between the outer cover and the wrap sheet, and/or between the surge layer and the wrap sheet. Moreover, adhesives placed between the wrap sheet and the inner liner reduce the absorbent property of the core by blocking the transport of fluids between these layers. The addition of an adhesive also increases the raw material costs associated with assembling disposable diapers. The standard adhesive loading is 0.31 to 0.33 grams of adhesive per diaper. Core integrity is not maintained at this loading. Additionally, it has been found that increasing the adhesive weight by tenfold, i.e., 3.1 to 3.3 grams per diaper does not appreciably improve core integrity.
Ultrasonically compressing the absorbent core between the inner liner and outer cover can be used in place of an adhesive to maintain the core integrity. Ultrasonic bonding involves high frequency mechanical energy transfers in the form of a reciprocating vertical motion. When ultrasonic energy is applied to several material layers, the vibrations within each material layer generate heat. Ultrasonic vibrations within a thermoplastic material will soften or melt the thermoplastic material if the heat generated increases the temperature of the thermoplastic material above the glass transition temperature or melting temperature, respectively. Thermoplastic materials are thus considered fusible.
The high crystallinity and high melting point of natural fibers makes these fibers infusible at the temperatures needed to soften or melt conventional thermoplastics. Since natural fibers are in general infusible, few attempts have been made to ultrasonically bond or weld a natural fiber core between two fusible materials. To ultrasonically bond a natural fiber core between two fusible materials, enough energy must be applied, and maintained within the layers, to fuse the fusible materials at the surface of the core, or to each other through the interstitial void volume in the core, without sufficiently deforming the fusible layers.
European Patent Application 0 438 113 A1 to S. J. Anapol et al. discloses an absorbent batt structure that has a discrete pattern of hydrogen bonded compressed portions formed on at least one surface of the batt. The batt contains fibers that are formed from a loose assemblage of cellulose, and, if needed, thermoplastic fibers, that has a discrete pattern of bonded compressed portions formed on at least one surface of the batt. These discrete compressions result in a batt structure with discrete density gradients, uniformly placed across the surface of the batt. These density gradients, in turn, result in enhanced fluid transfer between adjacent compressed portions, while substantially maintaining the absorbency of the batt. A water spray is applied to the surface of the batt and then an embossing roll, or ultrasonic energy, is applied to the surface to define a plurality of substantially, uniformly spaced, hydrogen-bonded compressed portions. Here, the core only is compressed and assembled into the final product, and a water spray is required to form the compressions in the core. Thus, a costly intermittent compression step is needed. The water spray may be needed to provide water molecules for hydrogen bond formation.
Other work involving absorbent articles disclose an actual fusion, or mechanical bonding of the material layers, as opposed to a pure compression of the these layers. For example, U.S. Pat. Nos. 4,823,783 and 5,059,277 to W. Willhite et al. disclose a method and apparatus for ultrasonically bonding continuous moving webs to one another using a stationary vibrating horn and a slick, thermally resistant slip layer. The slip layer is placed between the webs and the horns to prevent web damage. In this method, at least one of the webs to be bonded is comprised of a polymeric material which can be locally melted or softened by the input of mechanical energy. The slip layer maximizes heat retention in the web to be bonded, and ensures that neither the relatively delicate polymeric webs or the more resilient highly compressible webs are damaged in the bonding process. Two or more webs can be bonded together, but the protective slip layer is not bonded to the resultant laminate structure. The nature of the bond formed between one or more heat softened polymeric webs and other layers in the structure will vary depending on the chemical makeup of the other layers. If one or more layers does not soften by the input of mechanical energy, but exhibits significant interstitial void volume, the bonding will likely comprise mechanical entanglements of the melted or softened polymeric webs with the infusible web or webs, and/or the fusing of the polymeric webs to one another through the interstitial void volume in the infusible web.
U.S. Pat. Nos. 5,269,860 discloses the fusion of a thermoplastic sheet onto a thermoplastic or a non-thermoplastic fibrous textile. The thermoplastic sheet can be ultrasonically fused to a textile substrate that has an equivalent or higher melting temperature than the thermoplastic sheet. Ultrasonic energy is applied to the thermoplastic sheet, and the sheet melts before the textile surface begins to soften. This results in a fusion between the melted thermoplastic and the textile fibers. The ultrasonic energy can be applied to localized sections of the thermoplastic sheet to form various patterns of the fused thermoplastic sheet and fiber substrate. U.S. Pat. No. 5,609,702 to V. E. Andersen discloses a method for mutually bonding at least two moving continuous webs to form a laminate containing at least one puckered material layer. These webs can be bonded by thermal or ultrasonic techniques. At least one of the webs comprises weldable material; however, the preferred approach is to bond webs, each containing a weldable material.
Other work in the area of articles containing an absorbent core have combined natural fibers with heat-fusible thermoplastic fibers, or other polymer additives, to improve the fusion and compression of the core. The application of thermal or ultrasonic energy to the combined core, or to substrates adjacent to the core, thermally fuses the thermoplastic material present in the core to other fibers within the core, and to other thermoplastic materials at the interface of the core, respectively. However, the inclusion of hydrophobic thermoplastic materials in the core within the voids and interstitial spaces reduces moisture intake and rate of wicking. Moreover, the addition of thermoplastic fibers to a natural fiber core adds additional expense to the fabrication of the disposable product. Examples of such systems of the prior art are disclosed in U.S. Pat. No. 4,886,697 to L. E. Perdelwitz, et al.; U.S. Pat. Nos. 4,844,965 and 4,939,017 to C. Foxman; and International Patent Application WO 98/27904 to K. S. Lynardet al.
Thus, there is a need for disposable diapers having improved absorbent core integrity upon wear, while maintaining the absorption capacity of the natural fiber core.
There is also a need to reduce costs in the manufacturing of these articles by eliminating or reducing the amount of adhesives in the final product, and by eliminating costly and intermittent bonding procedures.
Therefore, there is a need in the art to improve the continum of the absorbent core without increasing material and manufacturing costs associated with these products.
There is also a need to eliminate additional material components, such as adhesives, and intermittent bonding procedures.
Further, there is also a need to maintain the core absorbency of the intact core in terms of the amount of fluid intake and its retention.
The present invention is directed to disposable care products that, upon use, maintain a better core integrity and absorption and methods for their production. These products eliminate the need for additional material components, such as adhesives, and intermittent bonding procedures. Further, these products maintain the core absorbency of the intact core in terms of the amount of fluid intake and its retention.
In one aspect, the present invention comprises a disposable personal care product having improved absorbent core integrity upon wear. The product comprises a liquid permeable inner liner, a liquid impermeable outer, a natural fiber core positioned between the inner liner and outer cover, and a region containing a plurality of localized compressions formed by ultrasonically compressing the natural fiber core between, although not necessarily adjacent to, at least one upper and at least one underlying fusible material.
In another aspect, the present invention comprises a method of making a disposable personal care article having improved absorbent core integrity upon wear. The method comprises positioning a natural fiber core between, but not necessarily adjacent to, a liquid permeable inner liner and a liquid impermeable outer cover. Next, a region containing a plurality of localized compressions is formed by ultrasonically compressing the natural fiber core between, although not necessarily adjacent to, at least one upper and at least one underlying fusible material. The periphery of the article is then bonded by conventional means, such as adhesives, crimping or fusing.
This process reduces costs associated with the manufacturing of such articles by eliminating or reducing the amount of adhesives in the final product, and by eliminating costly and intermittent bonding procedures. The method also improves the continuum of the absorbent core without increasing material and manufacturing costs associated with these products.
Thus, it is an object of the present invention to provide disposable personal care products having improved absorbent core integrity upon wear while maintaining the absorption capacity of the core.
It is another object of the invention to provide disposable personal care products having improved absorbent core integrity upon wear, containing a natural fibrous core that is ultrasonically compressed between at least one upper and at least one underlying fusible material.
It is yet another object of the present invention to provide disposable personal care products having improved absorbent core integrity upon wear that do not contain an adhesive at the inner planar surface, as opposed to the edges, of any material layer.
It is an object of the present invention to provide a method of making disposable personal care products having improved absorbent core integrity upon wear while maintaining the absorption capacity of the core.
It is another object of the invention to provide a method of making disposable personal care products having improved absorbent core integrity upon wear, containing a natural fibrous core that is ultrasonically compressed between at least one upper and at least one underlying fusible material.
It is yet another object of the present invention to provide a method of making disposable personal care products having improved absorbent core integrity upon wear that do not contain an adhesive at the inner planar surface, as opposed to the edges, of any material layer.
It is a further object of the present invention to provide a method of making disposable personal care products having improved absorbent core integrity upon wear by ultrasonically compressing, in one step, the natural fiber absorbent core between at least one upper and at least one underlying fusible material.
It is an object of the present invention to provide a method of making disposable personal care products having improved absorbent core integrity upon wear by ultrasonically compressing, in one step, the natural fiber absorbent core between at least one upper and at least one underlying fusible material, and applying the ultrasonic energy to only one of the fusible materials.
It is another object of the present invention to provide a method of making disposable personal care products having improved absorbent core integrity upon wear, by ultrasonically compressing, in one step, the natural fiber absorbent core between at least one upper and at least one underlying fusible material, and applying the ultrasonic energy to only one of the fusible materials after the assembly of all the product""s material layers.
These and other objects of the present invention will be more readily apparent when considered in reference with the following description.